Previous work from this laboratory has established that the regulation of polyamine metabolism is altered in mouse epidermal tumors produced by an initiation-promotion protocol compared to normal or hyperplastic epidermis. The significance of these alterations in an important growth- associated metabolic pathway is not known. The overall goal of this project is to test the hypothesis that disruption of cellular controls on polyamine biosynthesis contributes to neoplastic development. To accomplish this goal, the following specific aims are proposed: 1. We will analyze the importance of ornithine decarboxylase (ODC) for both normal epidermal homeostasis and for tumor development in skin, using a newly developed chimeric mouse model. The role of polyamine synthesis and accumulation in tumor promotion will be directly tested by using transgenic mice genetically engineered to target overexpression of ODC to specific cell populations within the epidermis. 2. The role of a newly discovered epidermal urea cycle in maintaining high tissue levels of ornithine will be evaluated in the Spfash ("Sparse fur abnormal skin and hair") mutant mouse strain. These mice, deficient in the key urea cycle enzyme ornithine transcarbamylase, will be used in tumor induction experiments to test the hypothesis that effective tumor promotion in mouse skin requires a functional urea cycle. 3. Our work in human colorectal adenocarcinomas documenting the presence of a GTP-activatable ODC isoform similar in properties to the previously described mouse epidermal tumor isoform will be extended by correlating the presence or absence of this isoform with clinical outcomes such as disease recurrence and patient survival. In addition, the presence of a GTP-activatable ODC will be correlated with genetic alterations implicated in colon carcinogenesis, such as mutations in the p53, c-Ki-ras, and MCC genes. The identification of critical intracellular pathways that become deregulated early in neoplastic development will undoubtedly have an impact in both basic and clinical research. Our work has the potential to not only clarify the role of polyamines in normal epidermal physiology but also to identify differences in polyamine metabolism between normal and premalignant tissue that might be clinically exploited for the benefit of human cancer patients.